Control system



Oct. 5, 1943. r; REAGAN 2,331,229

CONTROL SYSTEM Filed Aug. 12, 1942 WITNESSES: INVENTOR Patented Oct. 5, 1943 CONTROL srs'rEM Maurice E. Reagan, Pittsburgh, Pa., assignor to Westinghouse Electric & Manufacturirg Company, East Pittsburgh, Pa., in corporation of Pennsylvania Application" August 12, 1942, Serial No. 454,535

9 Claims.

My invention relates, generally, to control systems, and it has reference in particular to timecycle control systems.

Generally stated, it is an object of my invention to provide, in a simple and effective manner for improving the operating characteristics of control systems utilizing relatively movable contact members for connecting relatively lowresistance devices to sources of electrical energy.

More specifically, it is an object of my invention to provide for limiting the initial and. final current flow through each of the contact members of face plate controllers to prevent burning of the leading and trailing edges of the contact members.

It is also an object of my invention to provide for using common control means with a plurality of devices connected to the contact membersv of a face plate type controller to prevent full 'energization of the devices for a predetermined time.

after contact is initially made with a contact member and to reduce the energization thereof a predetermined time before contact with the consistance of the energizing circuits of each of a,

number of control devices energized by a face plate type contact device having slidably engagingcontact members, during the initial and final stages of engagement of the contact members.

Yet another object of my invention is to provide for rendering a relatively high resistance device connected in series with each of a number of relatively low resistance control devices inefle'ctive for an interval of time intermediate the initial and final stages of energization ofeach device. l l

Other objects will, in part, be obvious and will, in part, be explained hereinafter.

According to my invention, burning of the leadingand trailing edges of the contact mem bers of a face plate type cycle controller may be readily prevented. The impedance of the circuits through the contact members is increased by connecting the relatively high resistance operatingwinding of a control relay in series with the A control operating winding of the control relay is rendered effective only during the initial and final stages of contact of the moving arm with each fixed contact member, thereby preventing burning of the contact members. v

For a more complete understanding of the na ture and scope of my invention, reference may be had to the following detailed description which maybe read in connection with the accompanying drawing, in which the single figure is a vdiagrammatic view of a time-cycle control system embodying the principal features of the inven-' tion'.

Referring to the single figure of the drawing,

the reference numeral it may denote generally a time-cycle control system wherein a plurality of load devices, such as for example, the valve motors it through I! are arranged to be connected to a suitable source 01' electrical energy by means of the conductors I8, I 9 and 21), 2t through the medium of aplurality of switch means 23 through 29 having operating windings 30 through 36. A line switch 3"! may be provided for co'n-- necting the system to, and disconnecting it from, the source. ling the energization of the windings 39 through 36 such'as the face plate type controller 38, which may have a contact arm 39 arranged to be rotated at a'substantially uniform speed to successively engage fixed contact members 40 through 46. A driving motor 48 may be provided for totating the arm 39 of the controller 38 and it may be reversibly connected by means of a reversing switch to the conductors 20 and 2!, in accordance with a familiar practice.

In order to prevent burning of the leading and trailing edges of the contact members 49 through 46 of the controller 38 as the arm 39 moves into and out of engagement with each contactmemher, control means maybe provided, denoted generally by the numeral 55. For example, a control relay 52 may be provided, having a relatively high resistance operating winding 53 normally; connected in series circuit relation with the moving contact arm 39 of the controller 38; The resistance of the operating winding 53 may be suficiently high to prevent operation of the switch means 23 through 29 from the deenergized to the energized position when the contact arm 39 initially engages any one of, the fixed contact members and connects the winding 53 in series therewith. The relay 52; however, may be designed to operate substantially as soon as the contact arm 39 engages any one of the contact members. Tlle resistance of the winding 53 should be low Means may be provided for control-' means-26.

fixed contact'members 453 through 45, means such as the control switch 55', may be provided. The operating winding 55 of the control switch 55 may be arranged for energization under the control of the control relay 52. For example, the operating winding 55 may be connected between the conductors 2t and 2! by means'of the normally open contact members 52a of the control relay 52. The control switch 55 may be provided with normally open contact members 55a arranged to provide a relatively low resistance shunt path about the operating winding 52 of the control relay. I

In orderto provide for operation of the control switch 55' only during an interval intermediate to the initial and final stages of contact of the arm 39 with any one of the contact members lilthrough 45, while the contact area therebetween is relatively small, suitable means may be provided for delaying the operation of the control switch. For example, energy storing means, such as the capacitor 53, may be connected in shunt relation with the operating winding 56 of the control switch to retard the energization of the winding 56 when first connected to the source, and to maintain the winding in an energized condition for a predetermined time after it has been disconnected from the source. A control resistor 59 may be provided for varying th e efiectof the capacitor 58 so as to vary the amount of delay imparted to'the operation of the control switch 55. r

Whenthe line switch 3'! is closed connecting the conductor 28 to the source, and when the contact arm 39 initially engages one of the fixed contact members, for example, the contact member 63, a circuit is completed from the conductor 2i through conductor 6i, operating winding 53, conductor 52, contact arm 39, contact memher 43, operating winding 33 of the switch means 2,5, and conductorv to the conductor 25.- Because of therelatively high resistance of the operating winding 53, insufiicient current flows in this circuit to eifect operation of the switch The control relay 52, however, operates, closing contact members 52a to provide an energizing circuit for the control switch 55.

Since the capacitor 58 is connected in' shunt relation-with the operating winding 56 of the control switch 55, a predetermined time delay occurs before the voltage across the winding 55 becomes sufiicient to eiTect operation of the control switch, during which relatively good contact is established between the contact arm 39 and the contact member 43. Accordingly, the contact members55a close a predetermined time after operation of the control relay 52 to provide a relatively low resistance shunt circuit about the relatively high resistance operating winding 53. Sufiicient current may now flow through the operating winding 33 of the switch means 26 to effect operation thereof. The switch means 26 thereupon operates, closing contact members 25a to connect the valve motor 14 to the source, and opening contact members 2522.

Upon the shunting of the winding 53 the control relay returns to the reenergized position, opening contact members 52a and 55 disconnecting the operating winding 55 of the control switch 55 from the source. Because of the charge stored by the capacitor 53, the control switch 55 is maintained in the energized position for a predetermined time interval after opening of the contact members 52a during which the moving contact arm 39 maintains relatively good contact with" the'fixed contact member 43. At the end of this time interval, the control switch 55 returns to the deenergized position, opening contact members 55a, and again inserting the relatively high resistance winding 53 in series circuit relation with the contact arm 39 and the fixed contact member 43. Thus during the final interval of contact the resistance of the circuit through the fixed contact member and the contact arm is relatively high. When the contact arm 39 finally disengages the contact member 43, the energizing circuit for the operating winding 33 of the switch means 25 is interrupted. Because of the relativelyhigh resistance of the operating winding 53, the current interrupted is of a relatively low value, though sufiicient to maintain the switch means 28 in the energized position, and little or no arcing orburning of the contact members occurs. When the contact arm 39 engages the next contact member, the above sequence repeats, so that the operating winding of the control relay is effective to reduce arcing and burning of the contact members each and every time the contact arm engages or disengages oneofthem.

From the above description and the-accompanying drawing, it will be apparentthat-Ihave provided for improving the operating characteristics of face plate type controllers, or other controllers having slidably engaging contact members, in a simple and effectivemanner. .Burning of the leading and trailing edges of the 0011-. tact members is efiectively'prevented with a minimum of apparatus and expense, By using the control means such as hereinbefore described, the intervals during which the impedance of the circuit made and interrupted by the moving and fixed contact members are increased, may be readily adjusted for 'difierent rates of operation.

of the moving contact .arm 39 so that the speed of operation of the entire system maybe readily varied while still retaining adequate protection against burning of the contact members.

Since certain changes, may be made in the,

above-described system and different embodiments of the invention may be made without de parting from the spirit or scope thereof, it is intended that all the subject matter shown in the accompanying drawing and included in the above description, shall be considered as illustrative and not in a limiting sense. .I

I claim as my invention: a 1. The combinationwith a plurality of fixed contact members dis'posed'to be connected to load circuits and arranged tobe'slidab1y engagedby a movable contact arm, of'relay means connected in series circuitwith the contact'arm to. increase the resistance of the load circuits, and means'controlling the connection. of .said lrelay means to provide forincreasingthejresistance of the load circuits during the initial, andfinal moments of contact of the arm with the tact member associated therewith. a a

the control device to a source of electrical ener y, control means connected in series with the contact members and control device to reduce the current flow therethrough, said control means being operable in response to the flow of a predetermined minimum current between the contact members, and additional control means energizable under the control of said control means for rendering said control means inefiective during the intermediate positions of the contact members.

3. A power system comprising, a load device, switch means connecting the load device to a source of electrical energy, contact means connected to control the energization of the switch means, circuit means connected in series relation with the contact means and the switch means including control means normally effective to increase the resistance of the circuit means, and additional control means controlled by said control means efiective to render said control means inefiective for a predetermined interval.

4. The combination with a relatively low resistance control device and sliding contact means therefor, of a control relay having a relatively high resistance operating winding connected in series relation with the contact means, switch means operable for a predetermined interval after the energization energizable under the control of the control relay to provide a relatively low resistance circuit about the relatively high resistance winding.

5. A control system for a load device comprising, switch means having a relatively low resistance operating winding energizable to connect the load device to a source of electrical energy, contact means having relatively slidable contacts controlling energization of the operating winding of the switch means, relay means having a relatively high resistance operating winding connected in series with the contacts to limit the current drawn by the operating winding of the switch means, and control means arranged for delayed operation upon energization and deenergization operable to provide a shunt circuit about the operating winding of the relay means during an intermediate portion of the interval of engagement of the contacts of the contact means.

6. The combination with a relatively low resistance device and relatively slidable contact means for connecting it to a, source of electrical energy, of control means having a relatively high resistance operating winding connected in series relation with the low resistance device and contact means, a control relay having an operating winding energizable under the control of the control means operable to provide a relatively low resistance shunt path about the relatively high resistance operating winding, and energy storage means connected in shunt relation with the operating winding of the control relay to provide delayed operation of the relay upon energization and deenergization.

7. Control means for a relatively low resistance device arranged to be energized through relatively slidable contact members comprising a relatively high resistance control device connected in series relation with the low resistance device and contact members effective to limit the current through the low resistance device, and switch means having delayed operating characteristics operable under the control of the control device to provide a relatively low resistance shunt around the relatively high resistance de vice during a predetermined interval intermedi ate the initial and final stages of contact of the contact members.

8. Control means for a relatively high current device connected to a source of electrical energy by relatively slidable contact members comprising, a control relay having a relatively high resistance operating winding connected in series relation with the device, and switch means operable under the control of the control relay to provide a relatively low resistance shunt path about the relatively high resistance operating winding, said switch means having delayed closing and opening characteristics whereby the impedance in series with the device is reduced for an interval intermediate the initial and final stages of contact of the contact members.

9. Circuit means for a time-cycle control system including a plurality of relatively low resistance control devices connected to fixed contact members arranged to be engaged by a movable contact member comprising, a control relay having a relatively high resistance operating winding connected in series with the movable contact member, switch means having an operating winding energizable under the control of the control relay operable to complete a relatively low resistance shunt circuit about the relatively high resistance operating winding, and a capacitor connected in shunt relation with the operating winding of the switch means.

MAURICE E. REAGAN. 

